<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
</head>
<body>
    <div id="app">
        <input type="text" v-model="n1"/>

        <select v-model="opt">
            <option value="+">+</option>
            <option value="-">-</option>
            <option value="*">*</option>
            <option value="/">/</option>
        </select>

        <input type="text" v-model="n2"/>

        <input type="button" value="=" @click="calc"/>

        <input type="text" v-model="result" />
    </div>

    <script>
        var vm = new Vue({
            el:'#app',
            data:{
                n1:0,
                n2:0,
                result:0,
                opt: '+'
            },
            methods:{
                calc(e){
                    // switch(this.opt){
                    //     case '+':
                    //     this.result = parseFloat(this.n1) + parseFloat(this.n2);
                    //     break;
                    //     case '-':
                    //     this.result = parseFloat(this.n1) - parseFloat(this.n2);
                    //     break;
                    //     case '*':
                    //     this.result = parseFloat(this.n1) * parseFloat(this.n2);
                    //     break;
                    //     case '/':
                    //     this.result = parseFloat(this.n1) / parseFloat(this.n2);
                    //     break;
                    // }
                    var codeStr = "parseFloat(this.n1) "+this.opt+" parseFloat(this.n2)";
                    this.result = eval(codeStr); // 执行字符串里的js代码
                }
            }
        })
    </script>
</body>
</html>